Volcanoes

What is a volcano? An opening in the earth's crust through which molten lava, ash, and gases are ejected. The opening in Earth’s surface which allows material to escape is called a vent.

How do Volcanoes form? Volcanoes form when molten rock from the mantle rises and leaks into the crust. The molten rock, called magma, rising from the mantle, gathers in a reservoir called the magma chamber. Eventually, but not always, the magma erupts onto the surface and forms lava.

Formation of a Volcano This is a drawing of magma making it's way up through the crust, causing the volcano to expand prior to eruption.

Where do Volcanoes form? At a Subduction Zone Along Hot Spots/plumes Along Divergent Plate Boundaries

What is Hot Spot? An area in the middle of a lithospheric plate where magma rises from the mantle and causes eruptions at the Earth's surface. If the hot spot forces magma to the surface during an eruption, it may create a volcano. Continual eruptions could eventually build a whole island on the surface. (Ex. Hawaii) The hot spot is stationary and the plate moves over it.

Hot spots cont…… Hot spots may cause the formation of geysers or hot springs, rather than lava based eruptions.

Hot Spot

Yellowstone Hot Spot Over the past 2 million years, the Yellowstone supervolcano has erupted every 600,000 years. It was 640,000 years ago when it last exploded. Another eruption, geologically speaking, is therefore threatening.

Five miles beneath Yellowstone, lies an immense pool of red hot magma Fed from the Earth’s mantle, it has been growing. This reservoir of magma and gas is now 31 miles long, 19 miles wide and 6 miles deep. The Yellowstone “hot spot” is considered to be the foundation of a rare “supervolcano” It is estimated that a supervolcano would erupt with the power at least 1000 times greater than an ordinary volcano.

Typical Volcano Structure

Types of Volcanic Eruptions Explosive: Short, violent eruptions that break lava into smaller pieces (cinders and ash) Effusive: Slow, continual eruptions of lava

Categories for Volcanoes Active – Has erupted in the last 100 years Dormant – Has erupted in the last 1000 years and is expected to erupt again Extinct – Hasn’t erupted in over 1000 years and is not expected to erupt again

Types of Volcanic Hazards Lava: Molten rock above the surface of Earth/exposed to oxygen Three categories based on characteristics: Aa Pahoehoe Pillow

1. Lava--Pahoehoe Lava that has a smooth, ropy surface. Typically thin, slow moving lava (150 ft/hr) Cools as a smooth, glassy surface

Pahoehoe

2. Lava-Aa Rigid, spiky lava Fast cooling, viscous (thick) Can moves as fast as 30 miles/hr Rough surface after cooling

Lava-Aa

Aa lava

3. Pillow Lava Lava is released under water Thick, slow moving eruptions Cold sea water rapidly solidifies lava into round, pillow-like shapes

Pillow Lava

Tephra Solid material that is ejected from the volcano ; particle size decreases as distance from volcano increases Ex. Cinders, ash, bomb Damage can include: lightening, respiratory problems, interference with aircraft, destruction of vegetation, building collapse

Tephra

Gases Poisonous Gases Gas developed as magma heats water vapor Chemicals are dissolved in water and evaporated as gas due to high temperatures Typical gases released: Carbon Dioxide, Sulfur Dioxide, Carbon Monoxide, Hydrochloric Acid May indicate impending eruption Poisonous in large amounts or to small creatures

Pyroclastic Flow What is it? – Fluidized masses of rock fragments and gases that move rapidly in response to gravity Facts: – Avalanche of material (gas/rock/debris) with very high temperature. Hazards: – Pyroclastic flows can incinerate, bury, and/or asphyxiate people. – Localized danger (if you are not in the path of the avalanche than you are not in danger)

Pyroclastic Flow

Lahar What is it? – Debris avalanches that contain water from snow and ice that melt and mix with loose debris Facts: – Can cause massive flooding along waterways – More widespread than pyroclastic flow Extremely dangerous for people living close to a volcanic eruption or near water associated with volcano

Lahar

Vocabulary 1.Volcano 2.Vent 3.Magma 4.Magma Chamber 5.Lava 6.Subduction Zone 7.Hot Spot 8.Aa Lava 9.Pahoehoe Lava 10.Pillow Lava 11.Tephra 12.Pyroclastic Flow 13.Lahar

Types of Volcanoes Composite/StratoVolcanoes Formed by Alternating layers of lava and ash Typically steep sided and have a high elevation. Explosive Eruptions Ex. Mount Fuji, Japan Mount St. Helens, WA

Types of Volcanoes cont….. Shield Volcanoes Formed by continuous eruption of lava over long periods of time. Usually very large at the base and not very steep. Effusive eruptions Ex. Mauna Loa and Kilauea in Hawaii

Example of Shield Volcano

Types of Volcanoes Cindercone Formed from the eruption of lava fragments called cinders. Usually form quite rapidly and are tall and steep sided. Not as tall as Strato and not as wide as Shield Ex. Mount Paricutin in Mexico

Cindercone